I have limited skills in linux, but I found the following link very useful:
Strange problem on startup - cannot open access to console.
In particular I took this sentence:
"The reason for this problem appearing seemingly out of the blue is fsck - the automated file system check, which runs on startup. During this check fsck may discover that something is wrong with some of your filesystems and interactive input is needed to confirm fixes. At this point it apparently attempts to launch the root shell via sulogin in order to ask for this input, sulogin then discovers that the root account has no password login privileges (i.e., its line in /etc/shadow has a * in the second field), and suggests to press "Enter" to continue."
Base on the explanation above (and taking a look at another cmdline.txt file from a different Rasberry that was working fine), before trying another thing, I added to the cmdline.txt file the following: fsck.repair=yes.
Now my cmdline.txt looks similar to:
dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=/dev/mmcblk0p7 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait splash plymouth.ignore-serial-consoles
That worked fine for me, but I recommend to make sure that doing that is not going to corrupt the system.